The Foreman prediction model is a common method applied to predict the tidal level of tidal stations which only have high and low water observations.But in the situation of different combination of tidal constituents,the dithering phenomenon will appear between the high and low tide,which increases false high or low tides,exerting dominant negative effects on predicting the times and heights of high and low water accurately and reducing the overall prediction accuracy of astronomical tide.Based on the characteristics (which include that first derivative at the point of each high and low tide is zero,the curve of which is convex at the high tide position and concave at the low) of astronomical tide curve of a certain tide station,an optimizing conformal tidal harmonic analysis model is established by the method of a piecewise polynomial interpolation,with only high and low water observations.This model,combined with the high and low tide data at Lianyungang station in Jiangsu province and Gaoqiao station in Shanghai,correspondingly contributes to the establishment of optimizing conformal tidal harmonic analysis model.The calculation results show that compared with the Foreman prediction model,the new model has great advantages of predicting the times and the heights of high and low tide.